The repair of lacerated or severed peripheral nerves using sutures is a common surgical procedure known as neurorrhaphy. The use of this sophisticated technique in recent years has enhanced the surgeon's ability to replant amputated body parts, to achieve composite tissue transfer, and to graft nerves. The success of such procedures is still limited because the current method of suturing severed nerves is difficult, time-consuming, and often yields poor functional results due to a variety of factors.
The increased trauma created by surgical manipulation and suturing is especially problematic in repairing nerves since trauma stimulates the formation of intraneural and extraneural connective tissue. Invasion of the repair or anastomotic site by connective tissue in turn prevents the regenerating axons in the proximal stump from entering the microscopic tubules contained in the distal stump. If a substantial number of axons are prevented from crossing the anastomotic site, neuroma (painful nerve cell tumor) formation often results. In addition, prospects for achieving significant reinnervation are reduced. The end result is lack of full return of motor and/or sensory function.
Recognition of this problem has prompted many researchers to explore alternatives to direct suturing in nerve repair and a variety of approaches involving the use of many different types of materials have been experimented with over the past 100 years.
All of these alternatives to direct suturing seek to protect the anastomotic site by wrapping, tubulizing, or otherwise encasing it with a natural or foreign substance, either absorbable or nonabsorbable. Since accurate alignment of the nerve stumps is important, most of these methods of treatment still require the use of some sutures which therefore reduces their effectiveness.
Sutureless tubulization techniques are known to be successful only in the case of very small, single fascicle nerves. The saphenous nerve in rats (0.3-0.5 mm diameter) was transected and repaired with a preformed tube or single leaf of collagen membrane as disclosed by J. M. Rosen, E. N. Kaplan, D. L. Jewett, and J. R. Daniels, "Fascicular Sutureless and Suture Repair of the Peripheral Nerves, A Comparison Study in Laboratory Animals", Orthopaedic Review 8 (4), 85 (1979). This method of repair avoids sutures but requires a totally tensionless situation to avoid retraction of the nerve stumps. J. M. Rosen in Orthopedic Transactions 6(1), 75(1982) reports that the peroneal nerve in rats (0.5-1.2 mm in diameter) was transected and repaired with a thin-walled, extruded tube of polyglycolic acid, cut open longitudinally along one wall. This method also requires a totally tensionless situation and is not advisable in the case of larger nerves since the tight fit required to maintain adequate nerve stump approximation would not provide for the release of pressure created by post-surgical swelling. The loose fit to accommodate swelling is an important feature of commercially available Silastic.TM. nerve cuffs, which must be used in combination with sutures (Bulletin: 14-393, Medical Products Division, Dow Corning Corp., Midland, Mich. 48640, April, 1969). Moreover, as shown in Example 6 below, longitudinally-split, extruded, smooth tubing used in sutureless repair on a 1.5 mm diameter rat sciatic nerve was found to be unsatisfactory due to retraction of the nerve.
Another approach to sutureless tubulization involves sucking the nerve stumps into a porous, metallic tube by means of a complex, vacuum actuated instrument, disclosed in U.S. Pat. Nos. 3,916,905 and 3,960,151. This method also risks the causing of compressive injury to the nerve upon post-surgical swelling in addition to the disadvantage of preventing the surgeon from observing the anastomotic site to ascertain correct rotational alignment.
A further example of avoiding sutures at the anastomotic site of nerve repair is provided by the use of "human fibrin glue" applied to the separated fascicles of a transected rat sciatic nerve positioned in the grooves of a metallic plate, disclosed by R. Ventura, et al., Ital. J. Orthop. Traumatol. (Italy) 6, (3) 407-414 (1981). In this case, the protective effect of the metal is present on only one side of the nerve. Moreover, the fibrin glue alone was not shown to be sufficient to prevent nerve stump retraction since the nerve stumps were anchored to the metal plate with epineural sutures.
Examples of tubulization materials that have been used in combination with sutures include silicone rubber as taught by R. D. Midgley and F. M. Woolhouse, "Silicone Rubber Sheathing as an Adjunct to Neural Anastomosis, Surgical Clinic of North America 48, 1149 (1968), and collagen as disclosed by D. G. Kline and G. J. Hayes, "The Use of a Resorbable Wrapper for Peripheral Nerve Repair, Experimental Studies in Chimpanzees", J. Neurosurgery 21, 737 (1964). Silicone has the disadvantages of being impermeable and nonabsorbable whereas the disadvantage of collagen is its potential antigenicity.
R. L. Reid, D. E. Cutright, and J. S. Garrison, "Biodegradable Cuff an Adjunct to Peripheral Nerve Repair: A Study in Dogs", U.S. Army Institute of Dental Research, Walter Reed Army Medical Center, Government Report ADA044491, Aug. 29, 1977, also published in The Hand 10, (3) 259 (1978), disclose the use of the biodegradable copolymer poly(glycolide-co-lactide), as smooth, rigid tubes for use as nerve cuffs. These authors were unable to show any improvement with the use of this device. Sutures were used in both control and experimental groups since the device was not capable of providing a sutureless repair. Hakan Molander et al., "Regeneration of Peripheral Nerve through a Polyglactin Tube", Muscle and Nerve 5, 54-57 (1982), reported less than satisfactory results in bridging nerve defects (missing portions of nerves) by use of a biodegradable polyglactin suture mesh shaped as a tube around the defect to serve as a framework for proliferating cells.
U.S. Pat. No. 3,937,223 teaches a partially-compressed, heat-embossed, flexible, tissue-absorbable, compacted, surgical hemostatic felt having specific fiber and density measurements which is in the form of a thin conformable mat.
Two related patents, U.S. Pat. Nos. 4,033,938 and 3,960,152, disclose bioabsorbable polymers of unsymmetrically substituted 1,4-dioxane-2,5-diones which are broadly stated in col. 9, lines 29-31 and in the bridging paragraph of cols. 9 and 10 ('938) and in col. 9, lines 20-23 and lines 51-65 ('152) to be useful as tubes or sheets for surgical repair such as nerve and tendon splicing. A similar disclosure in U.S. Pat. No. 4,074,366, col. 6, lines 13-16 and 43-57, relates to poly(N-acetyl-D-glucosamine), i.e. chitin. However, there is no enabling disclosure in the specifications or in their Examples as to how such tubes are to be prepared, the characteristics required, and their method of use.
None of these references teaches a body-absorbable, porous, rough-surfaced device which is in the form of a longitudinally-openable tube which can be utilized for repair of a nerve without the use of sutures.